1. Field of the Invention
The present invention generally relates to a novel method and an apparatus for preparing a transparent substrate with a patterned polymer layer formed thereon, and more particularly to a method and an apparatus for manufacturing a color filter for use in a liquid crystal display. And more specifically, the present invention relates to a flat color filter made by the novel method.
2. Description of Related Art
Color liquid crystal flat panel displays have been popularly employed recently in notebook type personal computers, monitors, televisions, and in many other pocketable devices, such as personal digit assistants(PDAs), mobile phones and so on. Generally, a color liquid crystal display comprises a backlight module for supplying a uniform surface light source, a color filter formed with a first electrode, a transparent substrate formed with a second counter electrode, a liquid crystal layer filled between the color filter and the transparent substrate to form a liquid crystal cell, first and second polarizer sheets disposed at opposite sides of the liquid crystal layer, a driving circuit, a signal and power supply controlling system. The liquid crystal cell, the first and second polarizer sheets cooperate to form a plurality of light valves for controlling flowing of light therethrough.
There are generally two types of the color filter popularly used in the liquid crystal displays: transmissive and transflective color filters. A typical transmissive color filter comprises a transparent substrate, and a color filter film formed on the transparent substrate. Each pixel of the color filter film is composed of red(R), green(G) and blue(B) sub-pixels. Each sub-pixel cell operates by transmitting or disrupting light by means of the light valve. The sub-pixels of the color filter is generally delimited by an opaque black matrix. When light passes through a sub-pixel of the color filter, all the unwanted colors are blocked, leaving only the specific corresponding color of the sub-pixel. A typical transflective type color filter is similar to the transmissive type color filter except that a patterned reflective film is interposed between the transparent substrate and the color filter film. The reflective film comprises a plurality of light transmitting units whereat backlight passes once through the color filter film, and a plurality of light reflective units whereat ambient light enters and reflected out of the display with the light passes twice through the color filter film. There is another type of transflective color display wherein the color filter film is made on a transparent substrate coated with partially reflective film. The partially reflective film consists of multiple layers of thin films, which allows certain portion of incident light to pass and reflects the rest. The color filter thus made is basically the same as the process for a transmissive type color filter.
On the whole, color filter is one of the most critical elements in determining the color image quality in a display, and the color filter takes a significant part in the overall cost for manufacturing liquid crystal display devices. Apart from being used in the liquid crystal displays, the color filters are also applicable to organic light emitting displays and plasma display panels.
Many efforts have been paid in the past to the development of low cost manufacturing methods with high performance product, but in this inventor's view, satisfactory result were hardly achieved. In the following paragraphs, typical known processes for preparing color filters will be discussed.
First, a dyeing process is known. With this process, a polymeric material is formed on a glass substrate as color reception layer. Thereafter, the colored pattern is formed by immersing the substrate in a dyeing bath for selectively coloring the color reception layer. Usually, additional photolithographic means were used to mask part of the color reception layer to guarantee no mix dyeing. This dyeing step is repeated three times for the three primary colors of red (R), green (G) and blue (B) to obtain a colored layer of R, G and B on the substrate.
Second, there is known a pigment dispersion process, and it is most popular in recent years. With this process, a photosensitive resin solution containing pigments in a dispersed state is applied on a substrate and dried to form a colored layer, then the layer is patterned via photolithographic means to produce a mono-color pattern. This pattern forming step is repeated three times to obtain a layer colored to the three primary colors of R, G and B.
Third, an electrodeposition process is known. With this process, a stripe type transparent electrode is formed on a substrate by photo etching process and a first color is produced by means of electrodeposition by immersing the patterned electrode into an electrodeposition coating solution containing a pigment, ED resin and an electrolyte solvent system, and with selective stripe electrodes for one color electrically connected in the circuit loop. Then, this step of producing a color is repeated three times to form a colored layer of the three primary colors of R, G and B. Finally, the formed layer is baked and hardened to complete the process.
Fourth, there is known a printing process using colored ink with pigments dispersed in thermosetting or UV curable resin, repeating a printing operation three times for the three primary colors of R, G and B and curing the resin to produce a colored layer.
What is common to all the above listed processes is that a same step has to be repeated three times for forming a colored layer of the three primary color of R, G and B and consequently increase the manufacturing cost. Additionally, a manufacturing method involving a large number of steps is normally accompanied by a low yield.